A Network Node and Mobile Device for Use in a Communication Network, Method of Operating the Same and Computer Program Products

ABSTRACT

According to one aspect, there is provided a method of operating a network node ( 10 ) in a communication network ( 2 ) to provide timing information for a mobile device ( 12 ), the network ( 2 ) defining an extended period that is longer than a predefined period in the network ( 2 ), the predefined period in the network ( 2 ) corresponding to the time taken to transmit a predefined plurality of frames, the method comprising broadcasting ( 101 ) a plurality of information blocks, IBs, to the mobile device ( 12 ), each IB indicating a current frame number in the predefined plurality of frames and a time reference bit, the time reference bit indicating whether the current predefined period is a particular one of a number of predefined periods in the extended period.

TECHNICAL FIELD

The technology described relates to communication networks, and inparticular to techniques for allowing mobile devices to operate with anextended system frame number (SFN) period, for example for the purposeof extending a discontinuous reception (DRX) period.

BACKGROUND

In a typical cellular radio system, radio or wireless terminals (alsoknown as mobile stations and/or user equipment units (UEs)) communicatevia a radio access network (RAN) to one or more core networks. The radioaccess network (RAN) covers a geographical area which is divided intocell areas, with each cell area being served by a base station, e.g., aradio base station (RBS), which in some networks may also be called, forexample, a “NodeB” (in a Universal Mobile Telecommunications System(UMTS) network) or “eNodeB” (in a Long Term Evolution (LTE) network). Acell is a geographical area where radio coverage is provided by theradio base station equipment at a base station site. Each cell isidentified by an identity within the local radio area, which isbroadcast in the cell. The base stations communicate over the airinterface operating on radio frequencies with the user equipment units(UEs) within range of the base stations.

In some radio access networks, several base stations may be connected(e.g., by landlines or microwave) to a radio network controller (RNC) ora base station controller (BSC). The radio network controller supervisesand coordinates various activities of the plural base stations connectedthereto. The radio network controllers are typically connected to one ormore core networks.

The Universal Mobile Telecommunications System (UMTS) is a thirdgeneration mobile communication system, which evolved from the GlobalSystem for Mobile Communications (GSM). Universal Terrestrial RadioAccess Network (UTRAN) is essentially a radio access network usingwideband code division multiple access (WCDMA) for user equipment units(UEs).

In a forum known as the Third Generation Partnership Project (3GPP),telecommunications suppliers propose and agree upon standards for thirdgeneration networks and UTRAN specifically, and investigate enhanceddata rate and radio capacity. The Third Generation Partnership Project(3GPP) has undertaken to evolve further the UTRAN and GSM based radioaccess network technologies. A number of releases for the EvolvedUniversal Terrestrial Radio Access Network (E-UTRAN) specification haveissued, and as with most specifications, the standard is likely toevolve. The Evolved Universal Terrestrial Radio Access Network (E-UTRAN)comprises the Long Term Evolution (LTE) and System ArchitectureEvolution (SAE).

Long Term Evolution (LTE) is a variant of a 3GPP radio access technologywhere the radio base station nodes are connected to a core network (viaAccess Gateways (AGWs)) rather than to radio network controller (RNC)nodes. In general, in LTE the functions of a radio network controller(RNC) node are distributed between the radio base stations nodes(eNodeBs in LTE) and AGWs. As such, the radio access network (RAN) of anLTE system has what is sometimes termed a “flat” architecture includingradio base station nodes without reporting to radio network controller(RNC) nodes.

A currently popular vision of the future of cellular networks includesmachines or other autonomous devices communicating between each other(or with an application server) without human interaction. A typicalscenario is to have sensors sending measurements infrequently, whereeach of the transmissions would consist of only small amounts of data.This type of communication is called machine-to-machine (M2M)communication in the literature, or machine-type communication (MTC), in3GPP.

UEs in cellular systems (such as 3GPP WCDMA, LTE) are most commonlybattery driven and the power consumption of these devices is thereforean important factor.

In the context of MTC, many of the devices are expected to be batteryoperated as well. Sensors and other devices may reside in remotelocations and the number of deployed devices could be so large that itwould be practically infeasible to replace or frequently recharge thebatteries in these kinds of devices. Thus, it is an important goal toaim for reduction in the power consumption when considering improvementsfor current cellular systems.

An existing means to reduce the battery power consumption is to usediscontinuous reception (DRX), a feature in which the UE's receiver isswitched off except at configured intervals.

Currently the longest specified DRX cycle lengths are 2.56 seconds and5.12 seconds for EUTRA and UTRA, respectively. However, it would bebeneficial to extend the DRX cycle lengths beyond currently specifiedvalues to further reduce the battery power consumption, especially forthe benefit of MTC devices where there is no possibility for interactivecharging of the battery on a regular basis. Although longer DRX cyclelengths naturally cause larger delays in the downlink, this is typicallynot a problem for delay insensitive traffic such as that generated byMTC devices.

However, the DRX cycle length is currently limited by a System FrameNumber (SFN) period. The SFN is used by UEs to keep synchronisation withthe network and is used as a timing reference. In LTE the SFN period is1024 radio frames equal to 10.24 seconds and in High-Speed Packet Access(HSPA) the SFN period is 4096 radio frames equal to 40.96 seconds.

In LTE a UE needs 10 bits to determine the SFN since it takes 1024different values. Eight of these bits are broadcast by the network in asystem frame number field in the master information block (MIB). The MIBis broadcast for 40 ms during which the same information (including thevalue in the system frame number field) is repeated four times, i.e.every 10 ms. As the MIB only carries eight of the bits for the SFN, thelast two bits, which gives four values for the SFN within the 40 msperiod, are retrieved implicitly by the UE from the different scramblingcodes used for the four copies of the MIB broadcast in each 10 msperiod.

SUMMARY

With a DRX cycle length longer than the SFN period (1024 radio framesequal to 10.24 seconds for LTE and 4096 radio frames equal to 40.96seconds for High-Speed Packet Access (HSPA)) there would have to be away to index the SFN periods in order to tell them apart within theextended DRX cycle length. For example, if the DRX cycle length for LTEwas extended to 40.96 seconds, it would be necessary to index the fourSFN periods occurring within that extended DRX cycle length in order forthe UE to tell them apart. This index can correspond to using additionalbits to extend the SFN range. If, for example, two index/expansion bitsare used, this could either be viewed as labelling each SFN period (1024frames) with an index from 1 to 4 or expanding the maximal SFN from 1024radio frames to 4096 radio frames. Note however that these additionalbits would only be read by UEs configured to operate with extended DRXsince legacy UEs (i.e. UEs configured according to earlier versions ofthe standards) would not be able to interpret SFN values larger than1024. Thus, it is necessary to find useful ways of communicating theseadditional SFN bits from the network to the UE.

One possible solution is to include the additional SFN bits in thesystem information (SI) that is broadcast by the network to the UEs. TheSI includes the MIB and other information required by the UEs tocommunicate reliably with the network. The other information isdistributed between different system information blocks (SIBs) which arescheduled in different ways. As indicated above, the eight bits of theSFN are placed in the MIB which is scheduled with a fixed period, withthe other two bits of the SFN being derived from the scrambling codeused with each copy of the MIB broadcast over a 40 ms period. Other SIsuch as Cell ID and cell barring information is placed in SystemInformation Block type 1 (SIB1), which is also scheduled periodicallybut with a different fixed periodicity to the MIB. There are variousother SIBs which contain other SI and are scheduled dynamically. Inorder to find the dynamically scheduled SIBs, the UE needs to acquire ascheduling list field which is included in SIB1 and which indicates thescheduling of the dynamically scheduled SIBs. In other words, theacquisition of other SIBs requires the acquisition of SIB type 1 first.

Thus, if the additional SFN bits are included in either an existing SIBor in a new SIB, which could be introduced for this purpose, a UE wouldfirst need to read SIB1 in order to obtain the scheduling information ofthe SIB containing the additional bits. That means, if a UE is waking upfrom a very long DRX cycle, the UE will typically need to read at leastthree information blocks in order to obtain the full extended SFN, whichwill have an adverse impact on the MTC UE's battery lifetime.

Even if the additional bits were put directly into SIB1, the requirementto read this SIB could have a bad enough impact on battery life to makeit unfeasible. This negative impact is illustrated in FIG. 1 (for aworst case scenario). The worst case scenario would be that SIB1 wouldhave to be read once every DRX cycle with a reading time of 80 ms, andassuming bad radio conditions plus a 10 ms sync time. Using a simplepower consumption model, the battery life is plotted against the DRXcycle length for this worst case scenario. In the model it is assumedthat SIB1 only has to be read for DRX cycle lengths longer than 10.24seconds which causes a discrete step in the curve. The other curves showthe battery life for two fixed start-up times before the transmission,10 ms and 100 ms. Not surprisingly, the battery life when SIB1 has to beread is equal to that of a fixed sync time of 10 ms before the discretestep and afterwards it is very close to that of a 100 ms fixed synctime.

In view of the problems with including the additional SFN bits in SIB1or other SIBs, it would be preferable to include the additional bits inthe MIB with the other SFN bits since the MIB is currently used by theUEs to obtain the SFN. However, since the MIB is broadcast veryfrequently, it is required to have a very small payload.

Currently, there are ten ‘spare’ bits in the MIB that do not have adefined function or purpose which could be used to indicate theadditional SFN bits. However, the spare bits are intended to allowEUTRAN to be enhanced with new features throughout its lifetime andcareful consideration must be given before allocating these bits to newpurposes.

Using more than, say, two of these bits may therefore be difficult,especially since only a relatively small fraction of all new UEs maymake use of (or be able to make use of) extended DRX cycles.Unfortunately, the gain in terms of battery life is rather modest ifonly one or a couple of bits are used. The document R2-131691 entitled“Analysis of standardization impacts of MTCe UEPCOP solutions” submittedby Ericsson and ST-Ericsson to RAN2#82 in Fukuoka, Japan on 20-24 May2013 models power consumption with extended DRX and suggests that theDRX cycle length should be increased by at least a factor of 10,requiring at least four additional SFN bits, in order to obtainsignificant gains, especially for long inter-arrival-times.

Thus, in summary, it is impractical or highly unlikely that enough ofthe spare bits in the MIB could be dedicated to purpose of extending DRXcycles. Using only one or two bits to extend the SFN and thus the DRXcycle would not provide sufficient battery consumption gains for, forexample, MTC devices.

In view of these difficulties with including additional bits to extendthe SFN in the MIB, aspects provide an alternative way of signalling anextended SFN. In particular, instead of transmitting one or moreadditional bits for the SFN, a single bit in the MIB (from the sparebits currently available) is used as a reference bit (called a ‘timereference bit’ or ‘time stamp’ herein) to indicate the first (or anotherspecified) SFN period in the extended SFN period. That is, where thistime reference bit is set to, say, ‘1’, this can indicate the MIB is inthe first (or another specified) SFN period in the extended SFN period,and the time reference bit will be set to, say, ‘0’ in the other SFNperiods making up the extended SFN period. In this way, a UE can keeptrack of an extended SFN index or additional SFN bits itself once itfinds this ‘time reference bit’ in an MIB.

Although the use of a time reference bit means that it can take the UE anumber of SFN periods before there is a wrap-around to the first (orother specified) SFN period and the first (or other specified) SFNperiod is identified, the trade-off is that only a single additional bitis required to be used in the MIB to signal an extended SFN period thatcan be many times the length of a conventional SFN period.

However, since the ‘time reference bit’ is set to the same value in eachMIB broadcast throughout each SFN period, it will be sufficient for theUE to read the MIB once per SFN period while searching for first (orspecified) SFN period. This means that a UE using DRX would effectivelyswitch to a shorter DRX cycle during this search (for example equal tothe conventional SFN period), which will only have a minor impact onbattery consumption (compared to the gains from using a longer DRX cycleenabled by the extended SFN period). Since the time stamp/time referencebit would be provided to the UE from the network (e.g. timinginformation such as the remaining time until the time reference bit isset) at radio resource control (RRC) connection setup or Hand-overreply, UEs would need to switch to this shorter DRX cycle for findingthe time reference bit only rarely (for example in the case ofrecalibration).

Thus, according to the above, the frequently broadcasted MIB, which UEsread anyway to obtain the SFN, can be used for the expansion of the SFNrange in order to have extended DRX cycles (i.e. extended beyond the SFNperiod), while requiring only one additional bit of information to bebroadcast. Providing extended DRX cycles in this way can provide largebattery consumption gains. It will be appreciated that the extended SFNrange can be used for other or additional purposes to providing extendedDRX cycles.

Although the techniques presented herein are described with reference toextending the SFN period to enable longer DRX cycles than the length ofthe conventional SFN period, it will be appreciated that an extended SFNperiod can be used for purposes other than DRX and is not restricted toUEs that use or that can use DRX (so for example it is not restricted toMTC UEs).

According to a specific aspect, there is provided a method of operatinga network node in a communication network to provide timing informationfor a mobile device, the network defining an extended period that islonger than a predefined period in the network, and each predefinedperiod in the network corresponding to the time taken to transmit apredefined plurality of frames. The method comprises broadcasting aplurality of information blocks, IBs, to the mobile device, each IBindicating a current frame number in the predefined plurality of framesand a time reference bit, the time reference bit indicating whether thecurrent predefined period is a particular one of a number of predefinedperiods in the extended period.

In some embodiments, the network node is to provide timing informationfor a mobile device operating in a discontinuous reception (DRX) mode,with a maximum DRX cycle period for the mobile device corresponding tothe length of the extended period, and the time reference bit indicateswhether the current predefined period is a particular one of the numberof predefined periods in the maximum DRX cycle period/extended period.

In some embodiments, the predefined periods in the network are systemframe number, SFN, periods and the frame number is an SFN. In someembodiments the predefined plurality of frames comprises 1024 or 4096frames.

In some embodiments, the time reference bit indicates whether thecurrent predefined period is the first one of the predefined periods inthe maximum DRX cycle period/extended (SFN) period.

In some embodiments, the one or more IBs are master information blocks,MIBs.

In some embodiments the step of broadcasting comprises incrementing thecurrent frame number with each broadcast of the IB. In the event thatthe current frame number is equal to the number of frames in thepredefined plurality, resetting the current frame number to an initialvalue for the next IB and determining the value for the time referencebit in the next IB according to whether the next predefined period isthe particular one of the predefined periods in the extended (SFN)period.

In some embodiments, the method further comprises the step oftransmitting an indication of the number of predefined periods until thetime reference bit is set to a mobile device.

In some embodiments, the step of transmitting the indication of thenumber of predefined periods is performed during setup of a mobiledevice. In other or further embodiments, the step of transmitting theindication of the number of predefined periods is performed duringhandover of a mobile device from another network node.

According to another specific aspect, there is provided a network nodefor use in a communication network, the network node being configured toprovide timing information for a mobile device, the network defining anextended period that is longer than a predefined period in the network,each predefined period in the network corresponding to the time taken totransmit a predefined plurality of frames. The network node comprises atransceiver module and a processing module; wherein the processingmodule is configured to control the transceiver module to broadcast aplurality of information blocks, IBs, to the mobile device, each IBindicating a current frame number in the predefined plurality of framesand a time reference bit, the time reference bit indicating whether thecurrent predefined period is a particular one of a number of predefinedperiods in the extended period.

According to another specific aspect, there is provided a network nodefor use in a communication network, the network node being for providingtiming information for a mobile device, the network defining an extendedperiod that is longer than a predefined period in the network, thepredefined period in the network corresponding to the time taken totransmit a predefined plurality of frames. The network node is adaptedto broadcast a plurality of information blocks, IBs, to the mobiledevice, each IB indicating a current frame number in the predefinedplurality of frames and a time reference bit, the time reference bitindicating whether the current predefined period is a particular one ofa number of predefined periods in the extended period.

According to another specific aspect, there is provided a network nodefor use in a communication network, the network node being for providingtiming information for a mobile device, the network defining an extendedperiod that is longer than a predefined period in the network, thepredefined period in the network corresponding to the time taken totransmit a predefined plurality of frames. The network node comprises aprocessor and a memory, said memory containing instructions executableby said processor whereby said network node is operative to broadcast aplurality of information blocks, IBs, to the mobile device, each IBindicating a current frame number in the predefined plurality of framesand a time reference bit, the time reference bit indicating whether thecurrent predefined period is a particular one of a number of predefinedperiods in the extended period.

Various embodiments of the above-defined network nodes are contemplatedin which the network node is adapted to or comprises instructionscontained in a memory to cause the network node to perform any of themethod embodiments described above.

According to another specific aspect, there is provided a method ofoperating a mobile device in a communication network, the networkdefining an extended period that is longer than a predefined period inthe network, the predefined period in the network corresponding to thetime taken to transmit a predefined plurality of frames. The methodcomprises operating a receiver in the mobile device to receive one ormore information blocks, IBs, broadcast by a network node in thecommunication network, each IB indicating a respective current framenumber in the predefined plurality of frames and a time reference bit,the time reference bit indicating whether the current predefined periodis a particular one of a number of predefined periods in the extendedperiod; and, after receiving an IB with a time reference bit indicatingthat the current predefined period is the particular one of the numberof predefined periods in the extended period, processing the currentframe number in said IB to determine the current frame number in theextended period.

In some embodiments, the mobile device is operating in a discontinuousreception, DRX, mode in a communication network, with a maximum DRXcycle period for the mobile device corresponding to the length of theextended period, and the step of processing uses the time reference bitto determine the current frame number in the maximum DRX cycleperiod/extended period.

In some embodiments, the mobile device has a selected DRX cycle lengththat is longer than a predefined period up to the maximum DRX cycleperiod, and the step of processing uses the determined current framenumber in the maximum DRX cycle period to determine the current framenumber in the selected DRX cycle length.

In some embodiments, the predefined periods in the network are systemframe number, SFN, periods and the frame number is an SFN. In someembodiments the predefined plurality of frames comprises 1024 or 4096frames.

In some embodiments, the time reference bit indicates whether thecurrent SFN period is the first one of the SFN periods in the maximumDRX cycle period/extended SFN period.

In some embodiments, the one or more IBs are master information blocks,MIBs.

In some embodiments, the method further comprises the step of receivingan indication of the number of predefined periods until the timereference bit is set from the network node. In some embodiments, thestep of receiving the indication of the number of predefined periodsoccurs during the setup of the mobile device. In some embodiments, setupof the mobile device occurs when the mobile device is powered on. Inother or further embodiments, the step of receiving the indication ofthe number of predefined periods occurs during handover of the mobiledevice to the network node.

According to another specific aspect, there is provided a mobile devicefor use in a communication network, the network defining an extendedperiod that is longer than a predefined period in the network, eachpredefined period in the network corresponding to the time taken totransmit a predefined plurality of frames. The mobile device comprises areceiver or transceiver module and a processing module; wherein theprocessing module is configured to operate the receiver or transceiverto receive one or more information blocks, IBs, broadcast by a networknode in the communication network, each IB indicating a respectivecurrent frame number in the predefined plurality of frames and a timereference bit, the time reference bit indicating whether the currentpredefined period is a particular one of a number of predefined periodsin the extended period, and to process the current frame number in areceived IB to determine the current frame number in the extended periodafter receiving an IB with a time reference bit indicating that thecurrent predefined period is the particular one of the predefinedperiods in the extended period.

According to another specific aspect, there is provided a mobile devicefor use in a communication network, the network defining an extendedperiod that is longer than a predefined period in the network, thepredefined period in the network corresponding to the time taken totransmit a predefined plurality of frames. The mobile device comprises areceiver, and the mobile device being adapted to operate the receiver inthe mobile device to receive one or more information blocks, IBs,broadcast by a network node in the communication network, each IBindicating a respective current frame number in the predefined pluralityof frames and a time reference bit, the time reference bit indicatingwhether the current predefined period is a particular one of a number ofpredefined periods in the extended period; and, after receiving an IBwith a time reference bit indicating that the current predefined periodis the particular one of the number of predefined periods in theextended period, process the current frame number in said IB todetermine the current frame number in the extended period.

According to another specific aspect, there is provided a mobile devicefor use in a communication network, the network defining an extendedperiod that is longer than a predefined period in the network, thepredefined period in the network corresponding to the time taken totransmit a predefined plurality of frames. The mobile device comprises areceiver, a processor and a memory, said memory containing instructionsexecutable by said processor whereby said mobile device is operative tooperate the receiver in the mobile device to receive one or moreinformation blocks, IBs, broadcast by a network node in thecommunication network, each IB indicating a respective current framenumber in the predefined plurality of frames and a time reference bit,the time reference bit indicating whether the current predefined periodis a particular one of a number of predefined periods in the extendedperiod; and, after receiving an IB with a time reference bit indicatingthat the current predefined period is the particular one of the numberof predefined periods in the extended period, process the current framenumber in said IB to determine the current frame number in the extendedperiod.

Various embodiments of the above-defined mobile devices are contemplatedin which the mobile device is adapted to or comprises instructionscontained in a memory to cause the mobile device to perform any of themethod embodiments described above.

Yet another aspect provides a computer program product having computerreadable code embodied therein, the computer readable code beingconfigured such that, on execution by a suitable computer or processor,the computer or processor is caused to perform any of the methodembodiments described above.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph illustrating the battery life for different DRX cyclelengths when SIB1 has to be read each time that a UE wakes up from DRXcompared to fixed sync times of 10 ms and 100 ms;

FIG. 2 is a non-limiting example block diagram of an LTE cellularcommunications network;

FIG. 3 is a block diagram of a mobile device according to an embodiment;

FIG. 4 is a block diagram of a base station according to an embodiment;

FIG. 5 is a block diagram of a core network node according to anembodiment;

FIG. 6 is a schematic illustration of the use of a time reference bit toextend an SFN period;

FIG. 7 is a flow chart illustrating a method of operating a network nodeaccording to an embodiment;

FIG. 8 is a flow chart illustrating a method of operating a mobiledevice according to an embodiment;

FIG. 9 is a schematic illustration of the use of a time reference bitand index bit to extend an SFN period;

FIG. 10 is a schematic illustration of an alternative use of a timereference bit and index bit to extend an SFN period;

FIG. 11 is a schematic illustration of the use of multiple timereference bits to extend an SFN period; and

FIG. 12 is a schematic illustration of an alternative use of multipletime reference bits to extend an SFN period.

DETAILED DESCRIPTION

The following sets forth specific details, such as particularembodiments for purposes of explanation and not limitation. But it willbe appreciated by one skilled in the art that other embodiments may beemployed apart from these specific details. In some instances, detaileddescriptions of well known methods, nodes, interfaces, circuits, anddevices are omitted so as not obscure the description with unnecessarydetail. Those skilled in the art will appreciate that the functionsdescribed may be implemented in one or more nodes using hardwarecircuitry (e.g., analog and/or discrete logic gates interconnected toperform a specialized function, ASICs, PLAs, etc.) and/or using softwareprograms and data in conjunction with one or more digitalmicroprocessors or general purpose computers. Nodes that communicateusing the air interface also have suitable radio communicationscircuitry. Moreover, the technology can additionally be considered to beembodied entirely within any form of computer-readable memory, such assolid-state memory, magnetic disk, or optical disk containing anappropriate set of computer instructions that would cause a processor tocarry out the techniques described herein.

Hardware implementation may include or encompass, without limitation,digital signal processor (DSP) hardware, a reduced instruction setprocessor, hardware (e.g., digital or analog) circuitry including butnot limited to application specific integrated circuit(s) (ASIC) and/orfield programmable gate array(s) (FPGA(s)), and (where appropriate)state machines capable of performing such functions.

In terms of computer implementation, a computer is generally understoodto comprise one or more processors, one or more processing modules orone or more controllers, and the terms computer, processor, processingmodule and controller may be employed interchangeably. When provided bya computer, processor, or controller, the functions may be provided by asingle dedicated computer or processor or controller, by a single sharedcomputer or processor or controller, or by a plurality of individualcomputers or processors or controllers, some of which may be shared ordistributed. Moreover, the term “processor” or “controller” also refersto other hardware capable of performing such functions and/or executingsoftware, such as the example hardware recited above.

Although the description is given for user equipment (UE), it should beunderstood by the skilled in the art that “UE” is a non-limiting termcomprising any mobile or wireless device or node equipped with a radiointerface allowing for at least one of: transmitting signals in UL andreceiving and/or measuring signals in DL. A UE herein may comprise a UE(in its general sense) capable of operating or at least performingmeasurements in one or more frequencies, carrier frequencies, componentcarriers or frequency bands. It may be a “UE” operating in single- ormulti-RAT or multi-standard mode. As well as “UE”, the term “mobiledevice” is used interchangeably in the following description, and itwill be appreciated that such a device, particularly a MTC device, doesnot necessarily have to be ‘mobile’ in the sense that it is carried by auser. Instead, the term “mobile device” encompasses any device that iscapable of communicating with communication networks that operateaccording to one or more mobile communication standards, such as GSM,UMTS, LTE, etc.

A cell is associated with a base station, where a base station comprisesin a general sense any node transmitting radio signals in the downlink(DL) and/or receiving radio signals in the uplink (UL). Some examplebase stations, or terms used for describing base stations, are eNodeB,eNB, Node B, macro/micro/pico/femto radio base station, home eNodeB(also known as femto base station), relay, repeater, sensor,transmitting-only radio nodes or receiving-only radio nodes. A basestation may operate or at least perform measurements in one or morefrequencies, carrier frequencies or frequency bands and may be capableof carrier aggregation. It may also be a single-radio access technology(RAT), multi-RAT, or multi-standard node, e.g., using the same ordifferent base band modules for different RATs.

It should be noted that use of the term “network node” as used hereincan refer to a base station, such as an eNodeB, a network node in theRAN responsible for resource management, such as a radio networkcontroller (RNC), or a core network node, such as a mobility managemententity (MME).

The signalling described is either via direct links or logical links(e.g. via higher layer protocols and/or via one or more network nodes).For example, signalling from a coordinating node may pass anothernetwork node, e.g., a radio node.

It will be appreciated that although the following description of theembodiments relates to EUTRAN, the principle of using a time referencebit in an information block as described herein is equally applicable toUTRAN and similar wireless communication systems.

FIG. 2 shows an example diagram of an EUTRAN architecture as part of anLTE-based communications system 2. Nodes in the core network 4 includeone or more Mobility Management Entities (MMES) 6, a key control nodefor the LTE access network, and one or more Serving Gateways (SGWs) 8which route and forward user data packets while acting as a mobilityanchor. They communicate with base stations 10 referred to in LTE aseNBs, over an interface, for example an S1 interface. The eNBs 10 caninclude the same or different categories of eNBs, e.g. macro eNBs,and/or micro/pico/femto eNBs. The eNBs 10 communicate with each otherover an interface, for example an X2 interface. The S1 interface and X2interface are defined in the LTE standard. A UE 12 can receive downlinkdata from and send uplink data to one of the base stations 10 with thatbase station 10 being referred to as the serving base station of the UE12.

FIG. 3 shows a user equipment (UE) 12 that can be used in one or more ofthe non-limiting example embodiments described. The UE 12 may in someembodiments be a mobile device that is configured for machine-to-machine(M2M) or machine-type communication (MTC). The UE 12 comprises aprocessing module 30 that controls the operation of the UE 12. Theprocessing module 30 is connected to a receiver or a transceiver module32 (which comprises a receiver and a transmitter) with associatedantenna(s) 34 which are used to receive signals from or both transmitsignals to and receive signals from a base station 10 in the network 2.To make use of discontinuous reception (DRX), the processing module 30can be configured to deactivate the receiver or transceiver module 32for specified lengths of time. The user equipment 12 also comprises amemory module 36 that is connected to the processing module 30 and thatstores program and other information and data required for the operationof the UE 12.

FIG. 4 shows a base station 10 (for example a NodeB or an eNodeB) thatcan be used in example embodiments described. It will be appreciatedthat although a macro eNB will not in practice be identical in size andstructure to a micro eNB, for the purposes of illustration, the basestations 10 are assumed to include similar components. Thus, the basestation 10 comprises a processing module 40 that controls the operationof the base station 10. The processing module 40 is connected to atransceiver module 42 (which comprises a receiver and a transmitter)with associated antenna(s) 44 which are used to transmit signals to, andreceive signals from, user equipments 12 in the network 2. The basestation 10 also comprises a memory module 46 that is connected to theprocessing module 40 and that stores program and other information anddata required for the operation of the base station 10. The base station10 also includes components and/or circuitry 48 for allowing the basestation 10 to exchange information with other base stations 10 (forexample via an X2 interface) and components and/or circuitry 49 forallowing the base station 10 to exchange information with nodes in thecore network 4 (for example via the S1 interface). It will beappreciated that base stations for use in other types of network (e.g.UTRAN or WCDMA RAN) will include similar components to those shown inFIG. 3 and appropriate interface circuitry 48, 49 for enablingcommunications with the other network nodes in those types of networks(e.g. other base stations, mobility management nodes and/or nodes in thecore network).

FIG. 5 shows a core network node 6, 8 that can be used in the exampleembodiments described. The node 6, 8 comprises a processing module 50that controls the operation of the node 6, 8. The processing module 50is connected to components and/or circuitry 52 for allowing the node 6,8 to exchange information with the base stations 10 with which it isassociated (which is typically via the S1 interface). The node 6, 8 alsocomprises a memory module 56 that is connected to the processing module50 and that stores program and other information and data required forthe operation of the node 6, 8.

It will be appreciated that only the components of the UE 12, basestation 10 and core network node 6, 8 required to explain theembodiments presented herein are illustrated in FIGS. 3, 4 and 5.

As described above, an extended SFN period is provided that is longerthan a normal SFN period. The length of the extended SFN period istypically an integer multiple of the length of an SFN period. When usedfor DRX, the extended SFN period sets the maximum DRX cycle length for aDRX UE 12, although it will be appreciated that a particular UE 12 mayuse a DRX cycle length that is longer than a normal SFN period up to theextended SFN period. In order to signal the SFN within this extended SFNperiod to DRX UEs 12 (and non-DRX UEs 12 that are otherwise making useof the extended SFN period), a single bit is included in an informationblock, IB (e.g. a master information block (MIB)), along with thecurrent SFN for a ‘normal’ SFN period, with the time reference bitindicating whether the current SFN period is a specified one of the SFNperiods in the extended SFN period. The specified one of the SFN periodsin the extended SFN period signalled by the time reference bit can bethe first SFN period, the last SFN period, or an intermediate (e.g.second, third, etc.) SFN period as required according to the specificimplementation. However, the time reference bit is preferably used toindicate whether the SFN period is the first SFN period in the extendedSFN period.

In preferred implementations one of the spare bits defined in the MIB isused for the time reference bit.

FIG. 6 is a schematic illustration of the use of a time reference bit toextend an SFN period according to an embodiment. Each block 60represents an SFN period signalled in a master information block (MIB)(or other information block (IB) that is used to signal frame numbering)with SFN ranging from 0 to 1023. The 1024 values for SFN are indicatedto the UEs in the conventional manner, i.e. with an 8-bit System FrameNumber field, and the remaining two bits being derived by a UE 12 fromthe different scrambling codes used for the four copies of the MIBbroadcast in each 10 ms period.

In this embodiment, the extended SFN period/maximum DRX cycle length 62corresponds to the length of four SFN periods 60. The extended SFNperiod 62 in this embodiment is therefore 4096 frames. It will beappreciated that extended SFN periods 62 of alternative lengths can beformed corresponding to more or less than four SFN periods 60.

Within the extended SFN period 60 shown in FIG. 6, each of the SFNperiods is labeled 1-4 respectively (indicated by reference number 64).Each SFN period 60 also has an associated value for the time referencebit 66 that is included along with the current SFN (e.g. 768) in the MIBor other IB. In this embodiment, the time reference bit 66 is used toindicate the first SFN period 60 (SFN period 1) in the extended SFNperiod 62. Thus, the time reference bit is set to ‘1’ for MIBs broadcastin the first SFN period 60 in each extended SFN period 62. The timereference bit is set to ‘0’ in MIBs broadcast in the other SFN periods60 to indicate that these are not the first SFN period 60 in theextended SFN period 62. It will be appreciated that in someimplementations the significance of the ‘1’ and ‘0’ values for the timereference bit can be switched.

Where shorter or longer extended SFN periods 62 are desired to theembodiment shown in FIG. 6, it will be appreciated that the timereference bit 66 will be set to ‘0’ for the appropriate number of SFNperiods 60.

FIG. 7 illustrates a method of operating a network node, such as a basestation 10, according to an embodiment. In step 101, the network node 10(and in particular the processing module 40) forms an information block(IB) that indicates a current SFN and an appropriate value for the timereference bit 66 (e.g. ‘1’ if the SFN period is the particular SFNperiod in the extended SFN period 62 and ‘0’ otherwise) and broadcaststhe IB to UEs 12 in the cell of the node 10 using the transceiver module42.

The current SFN can then be incremented for broadcast in the next IB (itbeing appreciated that the value provided in the system frame numberfield in the MIB will be incremented by one following four repeats ofthe current value with the different scrambling codes). When the currentSFN reaches the end of the SFN period 60 (e.g. SFN=1023), the currentSFN value ‘wraps-around’ and returns to SFN=0 for the next SFN period60. In this case, the node 10 determines the value for the timereference bit 66 to be included in the MIB for each broadcast during thenext SFN period 60.

As noted above, it will be appreciated that the base station 10/network2 can define the extended SFN period 62 for the purpose of enablinglonger DRX cycles than the current maximum of an SFN period, as well asfor other purposes.

FIG. 8 illustrates a method of operating a mobile device, such as a UE12, according to an embodiment. In this illustrated embodiment the UE 12is operating in a discontinuous reception (DRX) mode with a selected DRXcycle period that is longer than the SFN period 60 up to the length ofthe extended SFN period 62 defined in the network 2 (which sets themaximum DRX cycle length). The length of the DRX cycle for the UE 12 istypically selected by the network 2, but in some cases it can beselected by the UE 12 itself. Operating in the DRX mode means that thereceiver or transceiver module 32 in the UE 12 is typically deactivatedor powered down and is only activated at specific intervals to receivepaging messages from the network 2. However, in order to ensure that theUE 12 activates the receiver or transceiver module 32 at the right time,the UE 12 needs to determine the current SFN within the extended SFNperiod 62 in order to synchronise with the network 2.

Thus, in step 111 the processing module 30 activates the receiver ortransceiver module 32 to receive an information block, IB, broadcast bya network node 10.

In step 113, the processing module 30 reads the IB to determine acurrent SFN (which as noted above can be determined by reading an 8-bitvalue in an SFN field in the IB and determining a further two-bit valuefrom the repetition of the MIB that the UE 12 is reading) and also atime reference bit 66. As noted above, the time reference bit 66indicates whether the current SFN period is the particular (e.g. first)SFN period in the extended SFN period 62.

In step 115, the processing module 30 determines whether the timereference bit 66 indicates that the current SFN period 60 is theparticular one of the plurality of SFN periods 60 in the extended SFNperiod 62. If not, the method returns to step 111 and the processingmodule 30 operates the receiver or transceiver module 32 at anappropriate time to receive another IB.

If the time reference bit 66 indicates that the current SFN period 60 isthe particular one of the plurality of SFN periods 60 in the extendedSFN period 62, the processing module 30 uses the fact that the currentSFN period 60 is the particular (e.g. first) SFN period 60 and the SFNindicated in the IB to determine the current SFN in the extended SFNperiod 62 (step 117). Once the current SFN in the extended SFN period 62is determined, the processing module 30 can determine the current framenumber in the selected DRX cycle length. The mobile device 12 is nowsynchronised with the extended SFN period and can now wake-up at theappropriate times to be paged by the network. Hence, when the mobiledevice 12 receives a subsequent MIB, the processing module 30 knowswhere in the extended SFN period 62 the current SFN period 60 lies, andcan determine the current SFN in the extended SFN period 62 from the SFNindicated in the MIB.

Although the method illustrated in FIG. 8 applies to a UE 12 operatingwith DRX, it will be appreciated that a similar method to that shown inFIG. 8 can be used by a non-DRX UE 12 to obtain synchronisation with theextended SFN defined in the network 2 for other purposes.

As indicated above, the use of the time reference bit 66 is analternative to having indexes for the SFN periods; with a reduction inthe number of broadcasted index bits required traded off against alonger time required for the UE 12 to get in sync with the network anddetermine the SFN in the extended SFN period 62 (since the UE 12 needsto receive an SFN in the particular SFN period 60 before synchronisationcan occur).

In some embodiments, a UE 12 entering a cell may have to stay in anactive receiving mode reading the MIB until the ‘time reference bit’(e.g. value ‘1’) is found in order to determine the full extended SFN inthe extended SFN period 62. This could potentially cause a reduction inbattery life.

In some embodiments, when a UE 12 is powered-on (or on occurrence ofanother event, such as when the UE 12 wishes to establish a connection,the network node 10 can signal the number of SFN periods 60 left untilthe next time the time reference bit 66 is set (i.e. to ‘1’) along withother information typically communicated to the UE 12 from the network 2at setup. Likewise, during hand-over to a new network node 10, theinformation on the number of SFN periods 60 left until the next time thetime reference bit 66 is set (in the target cell) could in the same waybe included the reply from the target cell (network node 10). In eithercase, as an alternative, if the extended SFN period is predetermined,the network node 10 can signal the number of SFN periods elapsed sincethe previous time the time reference bit 66 was set. In the embodimentsdescribed below where multiple time reference bits are used, the networknode 10 can signal the number of SFN periods 60 left until the next timeany of the time reference bits is set (and in some cases also indicatewhich of the time reference bits is set.

At cell-reselection, however, the UE 12 will need to wait for the timereference bit 66. However, since the time reference bit 66 is the samefor an entire SFN period 60, it would however be sufficient for the UE12 to only read the MIB once per SFN period 60, effectively meaning thatthe UE 12 switches to a shorter DRX cycle (i.e. a cycle that is equal toor less than an SFN period 60) until the time stamp (time reference bit)is found, which means that there would only be a minor impact on batteryconsumption in rare cases.

There is another reason (other than a slight increase in batteryconsumption in rare cases) not to have the time stamp bit set tooinfrequently; up until the point the UE 12 reads an IB with the timereference bit set it is not reachable by paging and consideredout-of-coverage by the network 2. The quality of service (QoS)requirement on the MTC UE 12 would then dictate the maximal DRX cyclelength that could be used. If all ten spare bits in the MIB were used asadditional bits for extending the SFN, for example, the maximal DRXcycle length would be 2.9 hours. Exactly the same DRX cycle length couldbe achieved with the time reference bit using only one bit. The downsidewould be that a UE 12 could in the worst case not be reachable by pagingfor almost 3 hours at cell reselection. To remedy or at least partiallymitigate this problem, a hybrid solution could be used in which anadditional one or more of the spare bits in the MIB could be used to geta finer granularity and/or different ‘time reference bits’. For example,with two bits instead of one a UE 12 would obtain synchronisation in athird of the time.

FIG. 9 illustrates a further embodiment in which an ‘index bit’ isprovided in addition to the time reference bit that can be used toindicate to a UE 12 which of two portions of the extended SFN period 62the current SFN period 60 is in. For example, the index bit can be usedto indicate whether the current SFN period 60 is in the first half orthe second half of the extended SFN period 62. This provides a UE 12that is not already synchronised with the network with an indication ofwhere it is in the extended SFN period 62, and enables the UE 12 toestimate the time that it may need to wake-up in order to receive a MIBin the SFN period 60 where the time reference bit 66 is set and thusobtain synchronisation.

The embodiment shown in FIG. 9 corresponds to the embodiment shown inFIG. 6, with the addition of an index bit 68 that is broadcast eachsystem frame. The index bit 68 can be broadcast in the MIB along withthe time reference bit 64, or it can be broadcast in a separateinformation block, such as a system information block, SIB.

In the embodiment of FIG. 9, the index bit 68 is used to distinguishbetween the first and second halves of the extended SFN period 62. Thatis, as the length of the extended SFN period 62 is equal to four SFNperiods 62, the index bit 68 can be set to ‘0’ in the first two SFNperiods 60 in the extended SFN period 62 and set to ‘1’ in the third andfourth SFN periods 60 in the extended SFN period 62 in order to indicateto the UE 12 which half of the extended SFN period 62 the current (i.e.received) SFN period 60 is in.

More generally, the extended SFN period 62 can be divided into twoportions through the use of an index bit 68, with the value of the indexbit 68 indicating to a UE 12 which portion of the extended SFN periodthe UE 12 is in. Therefore, in the example of FIG. 9, if the UE 12receives an MIB and the time reference bit 66 is set to ‘1’, it willknow that the current SFN period 60 is the first SFN period 60 in theextended SFN period 62 and it can determine the current SFN in theextended SFN period 62. Otherwise, if the time reference bit 66 is setto ‘0’, the UE 12 can examine the index bit 68 to determine which halfof the extended SFN period 62 the current SFN period 60 is in, anddetermine another time to wake-up and potentially receive a MIB that hasthe time reference bit 66 set.

In a further embodiment, the UE 12 can be configured to interpret thetime reference bit 66 and the index bit 68 together to further reducethe time required to obtain synchronisation. This embodiment isillustrated in FIG. 10. In this embodiment, the extended SFN period 62is the length of eight standard SFN periods 60. As described above, theindex bit 68 is used to indicate whether the current SFN 60 is in thefirst half or the second half of the extended SFN period 62. However, inthis embodiment, the time reference bit 66 is set to ‘1’ in one of theSFN periods 60 in the first portion (e.g. the first SFN period 60 of theextended SFN period 62) and also in an SFN period 60 in the secondportion of the extended SFN period 62 (e.g. the fifth SFN period 62 inthe extended SFN period 62).

In this embodiment, a UE 12 will be configured to read the timereference bit 66 and index bit 68 together to try and identify thecurrent SFN period 60 in the extended SFN period 62. In particular, inthis example, when the time reference bit 66 is ‘1’ and the index bit is‘0’ the UE 12 will know that the current SFN period 60 is the first SFNperiod in the extended SFN period 62, when both the time reference bitand the index bit are ‘1’ the UE 12 will know that the current SFNperiod 60 is the fifth SFN period in the extended SFN period 62.Otherwise, when the time reference bit 66 is set to ‘0’ the UE 12 willuse the index bit 68 to determine which portion of the extended SFNperiod 62 the current SFN period is in.

As indicated above, another way to achieve finer granularity and reducethe time required to achieve synchronisation is to use different timereference bits. In particular, two or more time reference bits can beprovided in the MIB or other information block, and the value of thesebits can code for different SFN periods 60 in the extended SFN period62. In some embodiments the first and second time reference bits can beinterpreted separately by a UE (i.e. each bit signals whether thecurrent SFN period is a specific respective SFN period).

FIG. 11 illustrates an embodiment in which two time reference bits areincluded in an MIB, and the time reference bits are read independentlyby the UE 12. In this embodiment, the first time reference bit 66corresponds to the time reference bit shown in FIG. 6 and thus indicateswhether the current SFN period 60 is the first SFN period 60 in theextended SFN period 62. A second time reference bit 70 is provided thatis used to indicate whether the current SFN period 60 is the third SFNperiod in the extended SFN period 62.

In other embodiments where multiple time reference bits are provided,the time reference bits can be interpreted together to represent one ofa number of different SFN periods. For example, with two time referencebits, the values ‘01’, ‘10’ and ‘11’ can represent three specific SFNperiods 60 in the extended SFN period 62. This reduces the time takenfor a UE to obtain synchronisation by a third compared to the use of asingle time reference bit. This embodiment is illustrated in FIG. 12. Inthis Figure, the extended SFN period 62 is the length of twelve SFNperiods 60 and the time reference bits 66, 70 together identify threespecific SFN periods 60. In particular, the values ‘01’, ‘10’ and ‘11’represent the first, fifth and ninth SFN periods 60 in the extended SFNperiod 62 respectively.

Modifications and other variants of the described embodiment(s) willcome to mind to one skilled in the art having the benefit of theteachings presented in the foregoing descriptions and the associateddrawings. Therefore, it is to be understood that the embodiment(s)is/are not to be limited to the specific examples disclosed and thatmodifications and other variants are intended to be included within thescope of this disclosure. Although specific terms may be employedherein, they are used in a generic and descriptive sense only and notfor purposes of limitation.

Various non-limiting embodiments are set out in the followingstatements:

1. A method of operating a network node in a communication network toprovide timing information for a mobile device, the network defining anextended period that is longer than a predefined period in the network,the predefined period in the network corresponding to the time taken totransmit a predefined plurality of frames, the method comprisingbroadcasting a plurality of information blocks, IBs, to the mobiledevice, each IB indicating a current frame number in the predefinedplurality of frames and a time reference bit, the time reference bitindicating whether the current predefined period is a particular one ofa number of predefined periods in the extended period.2. A method as in statement 1, wherein the predefined periods in thenetwork are system frame number, SFN, periods and the frame number is anSFN.3. A method as in statement 1 or 2, wherein the one or more IBs aremaster information blocks, MIBs.4. A method as in any of statements 1-3, wherein the method furthercomprises in the event that the current frame number is equal to thenumber of frames in the predefined plurality, setting the current framenumber for the next IB to an initial value and determining the value forthe time reference bit in the next IB according to whether the nextpredefined period is the particular one of the predefined periods in theextended period.5. A method as in any of statements 1-4, wherein the method furthercomprises transmitting an indication of the number of predefined periodsuntil the time reference bit is set to a mobile device.6. A method as in statement 5, wherein the step of transmitting theindication of the number of predefined periods is performed during setupof a mobile device or during handover of a mobile device from anothernetwork node.7. A method as in any of statements 1-6, the method further comprisingthe step of broadcasting an index bit for each IB that indicates whetherthe current predefined period is in a first portion or a second portionof the extended period.8. A method as in statement 7, wherein the step of broadcastingcomprises broadcasting the plurality of IBs with the time reference bitset in a particular one of the predefined periods in the first portionand a particular one of the predefined periods in the second portion.9. A method as in any of statements 1-6, wherein the step ofbroadcasting further comprises broadcasting each IB with a second timereference bit, the second time reference bit indicating whether thecurrent predefined period is another particular one of the number ofpredefined periods in the extended period.10. A computer program product having computer readable code embodiedtherein, the computer readable code being configured such that, onexecution by a suitable computer or processor, the computer or processoris caused to perform any of the methods in statements 1-9.11. A network node for use in a communication network to provide timinginformation for a mobile device, the network defining an extended periodthat is longer than a predefined period in the network, the predefinedperiod in the network corresponding to the time taken to transmit apredefined plurality of frames, the network node being adapted tobroadcast a plurality of information blocks, IBs, to the mobile device,each IB indicating a current frame number in the predefined plurality offrames and a time reference bit, the time reference bit indicatingwhether the current predefined period is a particular one of a number ofpredefined periods in the extended period.12. A network node as in statement 11, wherein the predefined periods inthe network are system frame number, SFN, periods and the frame numberis an SFN.13. A network node as in statement 11 or 12, wherein the one or more IBsare master information blocks, MIBs.14. A network node as in any of statements 11-13, wherein the networknode is adapted to set the current frame number for the next IB to aninitial value in the event that the current frame number is equal to thenumber of frames in the predefined plurality, and determine the valuefor the time reference bit in the next IB according to whether the nextpredefined period is the particular one of the predefined periods in theextended period.15. A network node as in any of statements 11-14, wherein the networknode is further adapted to transmit an indication of the number ofpredefined periods until the time reference bit is set to a mobiledevice.16. A network node as in statement 15, wherein the network node isadapted to transmit the indication of the number of predefined periodsduring setup of a mobile device or during handover of a mobile devicefrom another network node.17. A network node as in any of statements 11-16, wherein the networknode is further adapted to broadcast an index bit for each IB thatindicates whether the current predefined period is in a first portion ora second portion of the extended period.18. A network node as in statement 17, wherein the network node isadapted to broadcast the plurality of IBs with the time reference bitset in a particular one of the predefined periods in the first portionand a particular one of the predefined periods in the second portion.19. A network node as in any of statements 11-16, wherein the networknode is adapted to broadcast each IB with a second time reference bit,the second time reference bit indicating whether the current predefinedperiod is another particular one of the number of predefined periods inthe extended period.20. A method of operating a mobile device in a communication network,the network defining an extended period that is longer than a predefinedperiod in the network, the predefined period in the networkcorresponding to the time taken to transmit a predefined plurality offrames, the method comprising operating a receiver in the mobile deviceto receive one or more information blocks, IBs, broadcast by a networknode in the communication network, each IB indicating a respectivecurrent frame number in the predefined plurality of frames and a timereference bit, the time reference bit indicating whether the currentpredefined period is a particular one of a number of predefined periodsin the extended period; and after receiving an IB with a time referencebit indicating that the current predefined period is the particular oneof the number of predefined periods in the extended period, processingthe current frame number in said IB to determine the current framenumber in the extended period.21. A method as in statement 20, the method further comprising the stepof operating the mobile device in a discontinuous reception, DRX, mode,with a maximum DRX cycle period for the mobile device corresponding tothe length of the extended period.22. A method as in statement 21, wherein the step of operating themobile device in a DRX mode comprises operating the mobile device with aselected DRX cycle length that is longer than a predefined period up tothe maximum DRX cycle period, and the method further comprises the stepof using the determined current frame number in the extended period todetermine the current frame number in the selected DRX cycle length.23. A method as in any of statements 20-22, wherein the predefinedperiods in the network are system frame number, SFN, periods and theframe number is an SFN.24. A method as in any of statements 20-23, wherein the one or more IBsare master information blocks, MIBs.25. A method as in any of statements 20-24, wherein the method furthercomprises the step of receiving an indication of the number ofpredefined periods until the time reference bit is set from the networknode.26. A method as in statement 25, wherein the step of receiving theindication of the number of predefined periods occurs during the setupof the mobile device or during handover of the mobile device to thenetwork node.27. A method as in any of statements 20-26, the method furthercomprising the step of receiving an index bit for each IB that indicateswhether the current predefined period is in a first portion or a secondportion of the extended period.28. A method as in statement 27, wherein, after receiving an IB that hasa time reference bit indicating that the current predefined period isnot the particular one of the number of predefined periods in theextended period, the method further comprises determining whether thecurrent predefined period is in the first portion or the second portionfrom the received index bit.29. A method as in statement 27, wherein the time reference bitindicates whether the current predefined period is a particular one ofthe predefined periods in the first portion and a particular one of thepredefined periods in the second portion, and wherein the step ofprocessing comprises processing the current frame number and the indexbit in said IB to determine the current frame number in the extendedperiod.30. A method as in any of statements 20-26, wherein the step ofreceiving further comprises receiving a second time reference bit ineach IB, the second time reference bit indicating whether the currentpredefined period is another particular one of the number of predefinedperiods in the extended period, and, after receiving an IB with thesecond time reference bit indicating that the current predefined periodis the another particular one of the number of predefined periods in theextended period, the method further comprises processing the currentframe number in said IB to determine the current frame number in theextended period.31. A computer program product having computer readable code embodiedtherein, the computer readable code being configured such that, onexecution by a suitable computer or processor, the computer or processoris caused to perform any of the methods as in any of statements 20-30.32. A mobile device for use in a communication network, the networkdefining an extended period that is longer than a predefined period inthe network, the predefined period in the network corresponding to thetime taken to transmit a predefined plurality of frames, the mobiledevice comprising a receiver and the mobile device being adapted tooperate the receiver to receive one or more information blocks, IBs,broadcast by a network node in the communication network, each IBindicating a respective current frame number in the predefined pluralityof frames and a time reference bit, the time reference bit indicatingwhether the current predefined period is a particular one of a number ofpredefined periods in the extended period, and to process the currentframe number in a received IB to determine the current frame number inthe extended period after receiving an IB with a time reference bitindicating that the current predefined period is the particular one ofthe predefined periods in the extended period.33. A mobile device as in statement 32, wherein the mobile device isadapted to operate in a discontinuous reception, DRX, mode, with amaximum DRX cycle period for the mobile device corresponding to thelength of the extended period.34. A mobile device as in statement 33, wherein the mobile device isadapted to operate in a DRX mode with a selected DRX cycle length thatis longer than a predefined period up to the maximum DRX cycle period,and the mobile device is further adapted to use the determined currentframe number in the extended period to determine the current framenumber in the selected DRX cycle length.35. A mobile device as in any of statements 32-34, wherein thepredefined periods in the network are system frame number, SFN, periodsand the frame number is an SFN.36. A mobile device as in any of statements 32-35, wherein the one ormore IBs are master information blocks, MIBs.37. A mobile device as in any of statements 32-36, wherein the mobiledevice is further adapted to receive an indication of the number ofpredefined periods until the time reference bit is set from the networknode.38. A mobile device as in statement 37, wherein the mobile device isfurther adapted to receive the indication of the number of predefinedperiods during the setup of the mobile device or during handover of themobile device to the network node.39. A mobile device as in any of statements 32-38, wherein the mobiledevice is further adapted to receive an index bit for each IB thatindicates whether the current predefined period is in a first portion ora second portion of the extended period.40. A mobile device as in statement 39, wherein the mobile device isfurther adapted to determine whether the current predefined period is inthe first portion or the second portion from the received index bitafter receiving an IB that has a time reference bit indicating that thecurrent predefined period is not the particular one of the number ofpredefined periods in the extended period.41. A mobile device as in statement 39, wherein the time reference bitindicates whether the current predefined period is a particular one ofthe predefined periods in the first portion and a particular one of thepredefined periods in the second portion, and wherein the mobile deviceis further adapted to process the current frame number and the index bitin said IB to determine the current frame number in the extended period.42. A mobile device as in any of statements 32-38, wherein the mobiledevice is further adapted to receive a second time reference bit in eachIB, the second time reference bit indicating whether the currentpredefined period is another particular one of the number of predefinedperiods in the extended period, and to process the current frame numberin said IB to determine the current frame number in the extended periodafter receiving an IB with the second time reference bit indicating thatthe current predefined period is the another particular one of thenumber of predefined periods in the extended period.43. A network node for use in a communication network, the network nodebeing for providing timing information for a mobile device, the networkdefining an extended period that is longer than a predefined period inthe network, the predefined period in the network corresponding to thetime taken to transmit a predefined plurality of frames, the networknode comprising a processor and a memory, said memory containinginstructions executable by said processor whereby said network node isoperative to broadcast a plurality of information blocks, IBs, to themobile device (12), each IB indicating a current frame number in thepredefined plurality of frames and a time reference bit, the timereference bit indicating whether the current predefined period is aparticular one of a number of predefined periods in the extended period.44. A network node as in statement 43, wherein the predefined periods inthe network are system frame number, SFN, periods and the frame numberis an SFN.45. A network node as in statement 43 or 44, wherein the one or more IBsare master information blocks, MIBs.46. A network node as in any of statements 43-45, wherein the networknode is further operative to set the current frame number for the nextIB to an initial value in the event that the current frame number isequal to the number of frames in the predefined plurality, and determinethe value for the time reference bit in the next IB according to whetherthe next predefined period is the particular one of the predefinedperiods in the extended period.47. A network node as in any of statements 43-46, wherein the networknode is further operative to transmit an indication of the number ofpredefined periods until the time reference bit is set to a mobiledevice.48. A network node as in statement 47, wherein the network node isfurther operative to transmit the indication of the number of predefinedperiods during setup of a mobile device or during handover of a mobiledevice from another network node.49. A network node as in any of statements 43-48, wherein the networknode is further operative to broadcast an index bit for each IB thatindicates whether the current predefined period is in a first portion ora second portion of the extended period.50. A network node as in statement 49, wherein the network node isfurther operative to broadcast the plurality of IBs with the timereference bit set in a particular one of the predefined periods in thefirst portion and a particular one of the predefined periods in thesecond portion.51. A network node as in any of statements 43-48, wherein the networknode is further operative to broadcast each IB with a second timereference bit, the second time reference bit indicating whether thecurrent predefined period is another particular one of the number ofpredefined periods in the extended period.52. A mobile device for use in a communication network, the networkdefining an extended period that is longer than a predefined period inthe network, the predefined period in the network corresponding to thetime taken to transmit a predefined plurality of frames, the mobiledevice comprising a receiver, a processor and a memory, said memorycontaining instructions executable by said processor whereby said mobiledevice is operative to operate the receiver to receive one or moreinformation blocks, IBs, broadcast by a network node in thecommunication network, each IB indicating a respective current framenumber in the predefined plurality of frames and a time reference bit,the time reference bit indicating whether the current predefined periodis a particular one of a number of predefined periods in the extendedperiod, and to process the current frame number in a received IB todetermine the current frame number in the extended period afterreceiving an IB with a time reference bit indicating that the currentpredefined period is the particular one of the predefined periods in theextended period.53. A mobile device as in statement 52, wherein the mobile device isfurther operative to operate in a discontinuous reception, DRX, mode,with a maximum DRX cycle period for the mobile device corresponding tothe length of the extended period.54. A mobile device as in statement 53, wherein the mobile device isfurther operative to operate in a DRX mode with a selected DRX cyclelength that is longer than a predefined period up to the maximum DRXcycle period, and the mobile device is further adapted to use thedetermined current frame number in the extended period to determine thecurrent frame number in the selected DRX cycle length.55. A mobile device as in any of statements 52-54, wherein thepredefined periods in the network are system frame number, SFN, periodsand the frame number is an SFN.56. A mobile device as in any of statements 52-55, wherein the one ormore IBs are master information blocks, MIBs.57. A mobile device as in any of statements 52-56, wherein the mobiledevice is further operative to receive an indication of the number ofpredefined periods until the time reference bit is set from the networknode.58. A mobile device as in statement 57, wherein the mobile device isfurther operative to receive the indication of the number of predefinedperiods during the setup of the mobile device or during handover of themobile device to the network node.59. A mobile device as in any of statements 52-58, wherein the mobiledevice is further operative to receive an index bit for each IB thatindicates whether the current predefined period is in a first portion ora second portion of the extended period.60. A mobile device as in statement 59, wherein the mobile device isfurther operative to determine whether the current predefined period isin the first portion or the second portion from the received index bitafter receiving an IB that has a time reference bit indicating that thecurrent predefined period is not the particular one of the number ofpredefined periods in the extended period.61. A mobile device as in statement 59, wherein the time reference bitindicates whether the current predefined period is a particular one ofthe predefined periods in the first portion and a particular one of thepredefined periods in the second portion, and wherein the mobile deviceis further operative to process the current frame number and the indexbit in said IB to determine the current frame number in the extendedperiod.62. A mobile device as in any of statements 52-58, wherein the mobiledevice is further operative to receive a second time reference bit ineach IB, the second time reference bit indicating whether the currentpredefined period is another particular one of the number of predefinedperiods in the extended period, and to process the current frame numberin said IB to determine the current frame number in the extended periodafter receiving an IB with the second time reference bit indicating thatthe current predefined period is the another particular one of thenumber of predefined periods in the extended period.63. A network node for use in a communication network to provide timinginformation for a mobile device, the network defining an extended periodthat is longer than a predefined period in the network, the predefinedperiod in the network corresponding to the time taken to transmit apredefined plurality of frames, the network node comprising broadcastingmeans for broadcasting of a plurality of information blocks, IBs, to themobile device, each IB indicating a current frame number in thepredefined plurality of frames and a time reference bit, the timereference bit indicating whether the current predefined period is aparticular one of a number of predefined periods in the extended period.64. A mobile device for use in a communication network, the networkdefining an extended period that is longer than a predefined period inthe network, the predefined period in the network corresponding to thetime taken to transmit a predefined plurality of frames, the mobiledevice comprising receiver control means for operating a receiver in themobile device to receive one or more information blocks, IBs, broadcastby a network node in the communication network, each IB indicating arespective current frame number in the predefined plurality of framesand a time reference bit, the time reference bit indicating whether thecurrent predefined period is a particular one of a number of predefinedperiods in the extended period; and processing means for, afterreceiving an IB with a time reference bit indicating that the currentpredefined period is the particular one of the number of predefinedperiods in the extended period, processing the current frame number insaid IB to determine the current frame number in the extended period.The “broadcasting means” of the network node, as well as the “receivercontrol means” and “processing means” of the mobile device may in someembodiments be implemented as computer programs stored in memory (e.g.in the memory modules of FIG. 3 and FIG. 4 respectively) for executionby processors (e.g. the processing modules of FIG. 3 and FIG. 4respectively).Further embodiments of the above-defined network node and mobile deviceare contemplated in line with the various method and apparatusembodiments described above.65. A method of operating a network node in a communication network toprovide timing information for a mobile device, the network defining anextended period that is longer than a predefined period in the network,the predefined period in the network corresponding to the time taken totransmit a predefined plurality of frames, the method comprisingbroadcasting a plurality of information blocks, IBs, to the mobiledevice, each IB indicating a current frame number in the predefinedplurality of frames and one or more time reference bits, the one or moretime reference bits indicating whether the current predefined period isa particular one of a specified subset of predefined periods in a numberof predefined periods in the extended period.66. A method as in statement 65, wherein each IB comprises one timereference bit and the specified subset of predefined periods comprises asingle predefined period.67. A method as in statement 65, wherein each IB comprises two or moretime reference bits.Further embodiments of the method of operating a network node asdescribed in statements 2-7 are also contemplated.68. A network node for use in a communication network to provide timinginformation for a mobile device, the network defining an extended periodthat is longer than a predefined period in the network, the predefinedperiod in the network corresponding to the time taken to transmit apredefined plurality of frames, the network node being adapted tobroadcast a plurality of information blocks, IBs, to the mobile device,each IB indicating a current frame number in the predefined plurality offrames and one or more time reference bits, the one or more timereference bits indicating whether the current predefined period is aparticular one of a specified subset of predefined periods in a numberof predefined periods in the extended period.69. A network node as in statement 68, wherein each IB comprises onetime reference bit and the specified subset of predefined periodscomprises a single predefined period.70. A network node as in statement 68, wherein each IB comprises two ormore time reference bits.Further embodiments of the network node as described in statements 12-17are also contemplated.71. A method of operating a mobile device in a communication network,the network defining an extended period that is longer than a predefinedperiod in the network, the predefined period in the networkcorresponding to the time taken to transmit a predefined plurality offrames, the method comprising operating a receiver in the mobile deviceto receive one or more information blocks, IBs, broadcast by a networknode in the communication network, each IB indicating a respectivecurrent frame number in the predefined plurality of frames and one ormore time reference bits, the one or more time reference bits indicatingwhether the current predefined period is a particular one of a specifiedsubset of predefined periods in a number of predefined periods in theextended period; and after receiving an IB with the one or more timereference bits indicating that the current predefined period is aparticular one of the specified subset of predefined periods in theextended period, processing the current frame number in said IB todetermine the current frame number in the extended period.72. A method as in statement 71, wherein each IB comprises one timereference bit and the specified subset of predefined periods comprises asingle predefined period.73. A method as in statement 71, wherein each IB comprises two or moretime reference bits.Further embodiments of the method of operating the mobile device asdescribed in statements 21-27 are also contemplated.74. A mobile device for use in a communication network, the networkdefining an extended period that is longer than a predefined period inthe network, the predefined period in the network corresponding to thetime taken to transmit a predefined plurality of frames, the mobiledevice comprises a receiver, and the mobile device is adapted to operatethe receiver in the mobile device to receive one or more informationblocks, IBs, broadcast by a network node in the communication network,each IB indicating a respective current frame number in the predefinedplurality of frames and one or more time reference bits, the one or moretime reference bits indicating whether the current predefined period isa particular one of a specified subset of predefined periods in a numberof predefined periods in the extended period; and to process the currentframe number in said IB to determine the current frame number in theextended period after receiving an IB with the one or more timereference bits indicating that the current predefined period is aparticular one of the specified subset of predefined periods in theextended period.75. A mobile device as in statement 74, wherein each IB comprises onetime reference bit and the specified subset of predefined periodscomprises a single predefined period.76. A mobile device as in statement 74, wherein each IB comprises two ormore time reference bits.Further embodiments of the mobile device as described in statements33-39 are also contemplated.

1-62. (canceled)
 63. A method of operating a network node in acommunication network to provide timing information for a mobile device,the network defining an extended period that is longer than a predefinedperiod in the network, the predefined period in the networkcorresponding to the time taken to transmit a predefined plurality offrames, the method comprising: broadcasting a plurality of informationblocks, IBs, to the mobile device, each IB indicating a current framenumber in the predefined plurality of frames and a time reference bit,the time reference bit indicating whether the current predefined periodis a particular one of a number of predefined periods in the extendedperiod.
 64. The method of claim 63, wherein the predefined periods inthe network are system frame number, SFN, periods and the frame numberis an SFN.
 65. The method of claim 63, wherein the one or more IBs aremaster information blocks, MIBs.
 66. The method of claim 63, wherein themethod further comprises: in the event that the current frame number isequal to the number of frames in the predefined plurality, setting thecurrent frame number for the next IB to an initial value and determiningthe value for the time reference bit in the next IB according to whetherthe next predefined period is the particular one of the predefinedperiods in the extended period.
 67. The method of claim 63, wherein themethod further comprises: transmitting an indication of the number ofpredefined periods until the time reference bit is set to a mobiledevice.
 68. The method of claim 67, wherein the step of transmitting theindication of the number of predefined periods is performed during setupof a mobile device or during handover of a mobile device from anothernetwork node.
 69. The method of claim 63, the method further comprisingthe step of: broadcasting an index bit for each IB that indicateswhether the current predefined period is in a first portion or a secondportion of the extended period.
 70. The method of claim 69, wherein thestep of broadcasting comprises: broadcasting the plurality of IBs withthe time reference bit set in a particular one of the predefined periodsin the first portion and a particular one of the predefined periods inthe second portion.
 71. The method of claim 63, wherein the step ofbroadcasting further comprises broadcasting each IB with a second timereference bit, the second time reference bit indicating whether thecurrent predefined period is another particular one of the number ofpredefined periods in the extended period.
 72. A non-transitory computerreadable medium storing computer readable code, the execution which byprocessing circuitry of a network node in a communication networkconfigures the network node to provide timing information for a mobiledevice, wherein the network defines an extended period that is longerthan a predefined period in the network, the predefined period in thenetwork corresponding to the time taken to transmit a predefinedplurality of frames, said computer readable code including code toconfigure the processing circuitry to: broadcast a plurality ofinformation blocks, IBs, to the mobile device, each IB indicating acurrent frame number in the predefined plurality of frames and a timereference bit, the time reference bit indicating whether the currentpredefined period is a particular one of a number of predefined periodsin the extended period.
 73. A network node for use in a communicationnetwork to provide timing information for a mobile device, the networkdefining an extended period that is longer than a predefined period inthe network, the predefined period in the network corresponding to thetime taken to transmit a predefined plurality of frames, the networknode being adapted to: broadcast a plurality of information blocks, IBs,to the mobile device, each IB indicating a current frame number in thepredefined plurality of frames and a time reference bit, the timereference bit indicating whether the current predefined period is aparticular one of a number of predefined periods in the extended period.74. The network node of claim 73, wherein the predefined periods in thenetwork are system frame number, SFN, periods and the frame number is anSFN.
 75. The network node of claim 73, wherein the one or more IBs aremaster information blocks, MIBs.
 76. The network node of claim 73,wherein the network node is adapted to set the current frame number forthe next IB to an initial value in the event that the current framenumber is equal to the number of frames in the predefined plurality, anddetermine the value for the time reference bit in the next IB accordingto whether the next predefined period is the particular one of thepredefined periods in the extended period.
 77. The network node of claim73, wherein the network node is further adapted to transmit anindication of the number of predefined periods until the time referencebit is set to a mobile device.
 78. The network node of claim 77, whereinthe network node is adapted to transmit the indication of the number ofpredefined periods during setup of a mobile device or during handover ofa mobile device from another network node.
 79. The network node of claim73, wherein the network node is further adapted to broadcast an indexbit for each IB that indicates whether the current predefined period isin a first portion or a second portion of the extended period.
 80. Thenetwork node of claim 79, wherein the network node is adapted tobroadcast the plurality of IBs with the time reference bit set in aparticular one of the predefined periods in the first portion and aparticular one of the predefined periods in the second portion.
 81. Thenetwork node of claim 73, wherein the network node is adapted tobroadcast each IB with a second time reference bit, the second timereference bit indicating whether the current predefined period isanother particular one of the number of predefined periods in theextended period.
 82. A method of operating a mobile device in acommunication network, the network defining an extended period that islonger than a predefined period in the network, the predefined period inthe network corresponding to the time taken to transmit a predefinedplurality of frames, the method comprising: operating a receiver in themobile device to receive one or more information blocks, IBs, broadcastby a network node in the communication network, each IB indicating arespective current frame number in the predefined plurality of framesand a time reference bit, the time reference bit indicating whether thecurrent predefined period is a particular one of a number of predefinedperiods in the extended period; and after receiving an IB with a timereference bit indicating that the current predefined period is theparticular one of the number of predefined periods in the extendedperiod, processing the current frame number in said IB to determine thecurrent frame number in the extended period.
 83. The method of claim 82,the method further comprising the step of operating the mobile device ina discontinuous reception, DRX, mode, with a maximum DRX cycle periodfor the mobile device corresponding to the length of the extendedperiod.
 84. The method of claim 83, wherein the step of operating themobile device in a DRX mode comprises operating the mobile device with aselected DRX cycle length that is longer than a predefined period up tothe maximum DRX cycle period, and the method further comprises the stepof: using the determined current frame number in the extended period todetermine the current frame number in the selected DRX cycle length. 85.The method of claim 82, wherein the predefined periods in the networkare system frame number, SFN, periods and the frame number is an SFN.86. The method of claim 82, wherein the one or more IBs are masterinformation blocks, MIBs.
 87. The method of claim 82, wherein the methodfurther comprises the step of: receiving an indication of the number ofpredefined periods until the time reference bit is set from the networknode.
 88. The method of claim 87, wherein the step of receiving theindication of the number of predefined periods occurs during the setupof the mobile device or during handover of the mobile device to thenetwork node.
 89. The method of claim 82, the method further comprisingthe step of: receiving an index bit for each IB that indicates whetherthe current predefined period is in a first portion or a second portionof the extended period.
 90. The method of claim 89, wherein, afterreceiving an IB that has a time reference bit indicating that thecurrent predefined period is not the particular one of the number ofpredefined periods in the extended period, the method further comprisesdetermining whether the current predefined period is in the firstportion or the second portion from the received index bit.
 91. Themethod of claim 89, wherein the time reference bit indicates whether thecurrent predefined period is a particular one of the predefined periodsin the first portion and a particular one of the predefined periods inthe second portion, and wherein the step of processing comprisesprocessing the current frame number and the index bit in said IB todetermine the current frame number in the extended period.
 92. Themethod of claim 82, wherein the step of receiving further comprisesreceiving a second time reference bit in each IB, the second timereference bit indicating whether the current predefined period isanother particular one of the number of predefined periods in theextended period, and, after receiving an IB with the second timereference bit indicating that the current predefined period is theanother particular one of the number of predefined periods in theextended period, the method further comprises processing the currentframe number in said IB to determine the current frame number in theextended period.
 93. A non-transitory computer readable medium storingcomputer readable code, the execution of which by processing circuitryin a mobile device configure for operation in a communication networkthat defines an extended period that is longer than a predefined periodin the network that corresponds to the time taken to transmit apredefined plurality of frames, said computer readable code includingcode to configure the processing circuitry to: operate a receiver in themobile device to receive one or more information blocks, IBs, broadcastby a network node in the communication network, each IB indicating arespective current frame number in the predefined plurality of framesand a time reference bit, the time reference bit indicating whether thecurrent predefined period is a particular one of a number of predefinedperiods in the extended period; and after receiving an IB with a timereference bit indicating that the current predefined period is theparticular one of the number of predefined periods in the extendedperiod, process the current frame number in said IB to determine thecurrent frame number in the extended period.
 94. A mobile device for usein a communication network, the network defining an extended period thatis longer than a predefined period in the network, the predefined periodin the network corresponding to the time taken to transmit a predefinedplurality of frames, the mobile device comprising a receiver and themobile device being adapted to: operate the receiver to receive one ormore information blocks, IBs, broadcast by a network node in thecommunication network, each IB indicating a respective current framenumber in the predefined plurality of frames and a time reference bit,the time reference bit indicating whether the current predefined periodis a particular one of a number of predefined periods in the extendedperiod, and process the current frame number in a received IB todetermine the current frame number in the extended period afterreceiving an IB with a time reference bit indicating that the currentpredefined period is the particular one of the predefined periods in theextended period.
 95. The mobile device of claim 94, wherein the mobiledevice is adapted to operate in a discontinuous reception, DRX, mode,with a maximum DRX cycle period for the mobile device corresponding tothe length of the extended period.
 96. The mobile device of claim 95,wherein the mobile device is adapted to operate in a DRX mode with aselected DRX cycle length that is longer than a predefined period up tothe maximum DRX cycle period, and the mobile device is further adaptedto use the determined current frame number in the extended period todetermine the current frame number in the selected DRX cycle length. 97.The mobile device of claim 94, wherein the predefined periods in thenetwork are system frame number, SFN, periods and the frame number is anSFN.
 98. The mobile device of claim 94, wherein the one or more IBs aremaster information blocks, MIBs.
 99. The mobile device of claim 94,wherein the mobile device is further adapted to receive an indication ofthe number of predefined periods until the time reference bit is setfrom the network node.
 100. The mobile device of claim 99, wherein themobile device is further adapted to receive the indication of the numberof predefined periods during the setup of the mobile device or duringhandover of the mobile device to the network node.
 101. The mobiledevice of claim 94, wherein the mobile device is further adapted toreceive an index bit for each IB that indicates whether the currentpredefined period is in a first portion or a second portion of theextended period.
 102. The mobile device of claim 101, wherein the mobiledevice is further adapted to determine whether the current predefinedperiod is in the first portion or the second portion from the receivedindex bit after receiving an IB that has a time reference bit indicatingthat the current predefined period is not the particular one of thenumber of predefined periods in the extended period.
 103. The mobiledevice of claim 101, wherein the time reference bit indicates whetherthe current predefined period is a particular one of the predefinedperiods in the first portion and a particular one of the predefinedperiods in the second portion, and wherein the mobile device is furtheradapted to process the current frame number and the index bit in said IBto determine the current frame number in the extended period.
 104. Themobile device of claim 94, wherein the mobile device is further adaptedto receive a second time reference bit in each IB, the second timereference bit indicating whether the current predefined period isanother particular one of the number of predefined periods in theextended period, and to process the current frame number in said IB todetermine the current frame number in the extended period afterreceiving an IB with the second time reference bit indicating that thecurrent predefined period is the another particular one of the number ofpredefined periods in the extended period.
 105. A network node for usein a communication network that defines an extended period that islonger than a predefined period in the network, the predefined period inthe network corresponding to the time taken to transmit a predefinedplurality of frames, the network node being configured to provide timinginformation for a mobile device in the network and comprising aprocessor and a memory, said memory containing instructions executableby said processor whereby said network node is operative to: broadcast aplurality of information blocks, IBs, to the mobile device, each IBindicating a current frame number in the predefined plurality of framesand a time reference bit, the time reference bit indicating whether thecurrent predefined period is a particular one of a number of predefinedperiods in the extended period.
 106. The network node of claim 105,wherein the predefined periods in the network are system frame number,SFN, periods and the frame number is an SFN.
 107. The network node ofclaim 105, wherein the one or more IBs are master information blocks,MIBs.
 108. The network node of claim 105, wherein the network node isfurther operative to set the current frame number for the next IB to aninitial value in the event that the current frame number is equal to thenumber of frames in the predefined plurality, and determine the valuefor the time reference bit in the next IB according to whether the nextpredefined period is the particular one of the predefined periods in theextended period.
 109. The network node of claim 105, wherein the networknode is further operative to transmit an indication of the number ofpredefined periods until the time reference bit is set to a mobiledevice.
 110. The network node of claim 109, wherein the network node isfurther operative to transmit the indication of the number of predefinedperiods during setup of a mobile device or during handover of a mobiledevice from another network node.
 111. The network node of claim 105,wherein the network node is further operative to broadcast an index bitfor each IB that indicates whether the current predefined period is in afirst portion or a second portion of the extended period.
 112. Thenetwork node of claim 111, wherein the network node is further operativeto broadcast the plurality of IBs with the time reference bit set in aparticular one of the predefined periods in the first portion and aparticular one of the predefined periods in the second portion.
 113. Thenetwork node of claim 105, wherein the network node is further operativeto broadcast each IB with a second time reference bit, the second timereference bit indicating whether the current predefined period isanother particular one of the number of predefined periods in theextended period.
 114. A mobile device for use in a communicationnetwork, the network defining an extended period that is longer than apredefined period in the network, the predefined period in the networkcorresponding to the time taken to transmit a predefined plurality offrames, the mobile device comprising a receiver, a processor and amemory, said memory containing instructions executable by said processorwhereby said mobile device is operative to: operate the receiver toreceive one or more information blocks, IBs, broadcast by a network nodein the communication network, each IB indicating a respective currentframe number in the predefined plurality of frames and a time referencebit, the time reference bit indicating whether the current predefinedperiod is a particular one of a number of predefined periods in theextended period; and process the current frame number in a received IBto determine the current frame number in the extended period, afterreceiving an IB with a time reference bit indicating that the currentpredefined period is the particular one of the predefined periods in theextended period.
 115. The mobile device of claim 114, wherein the mobiledevice is further operative to operate in a discontinuous reception,DRX, mode, with a maximum DRX cycle period for the mobile devicecorresponding to the length of the extended period.
 116. The mobiledevice of claim 115, wherein the mobile device is further operative tooperate in a DRX mode with a selected DRX cycle length that is longerthan a predefined period up to the maximum DRX cycle period, and themobile device is further adapted to use the determined current framenumber in the extended period to determine the current frame number inthe selected DRX cycle length.
 117. The mobile device of claim 114,wherein the predefined periods in the network are system frame number,SFN, periods and the frame number is an SFN.
 118. The mobile device ofclaim 114, wherein the one or more IBs are master information blocks,MIBs.
 119. The mobile device of claim 114, wherein the mobile device isfurther operative to receive an indication of the number of predefinedperiods until the time reference bit is set from the network node. 120.The mobile device of claim 119, wherein the mobile device is furtheroperative to receive the indication of the number of predefined periodsduring the setup of the mobile device or during handover of the mobiledevice to the network node.
 121. The mobile device of claim 114, whereinthe mobile device is further operative to receive an index bit for eachIB that indicates whether the current predefined period is in a firstportion or a second portion of the extended period.
 122. The mobiledevice of claim 121, wherein the mobile device is further operative todetermine whether the current predefined period is in the first portionor the second portion from the received index bit after receiving an IBthat has a time reference bit indicating that the current predefinedperiod is not the particular one of the number of predefined periods inthe extended period.
 123. The mobile device of claim 121, wherein thetime reference bit indicates whether the current predefined period is aparticular one of the predefined periods in the first portion and aparticular one of the predefined periods in the second portion, andwherein the mobile device is further operative to process the currentframe number and the index bit in said IB to determine the current framenumber in the extended period.
 124. The mobile device of claim 114,wherein the mobile device is further operative to receive a second timereference bit in each IB, the second time reference bit indicatingwhether the current predefined period is another particular one of thenumber of predefined periods in the extended period, and to process thecurrent frame number in said IB to determine the current frame number inthe extended period after receiving an IB with the second time referencebit indicating that the current predefined period is the anotherparticular one of the number of predefined periods in the extendedperiod.